1. Field of Invention
The present invention relates to overload protectors for communications systems, and in particular, to overvoltage protection devices having back-up air gap protection.
2. Discussion of the Relevant Art
In communication systems, such as telephone systems, it is necessary to position overload protectors at various positions to protect sensitive parts of the system to protect equipment attached to the line from lightning strikes or other cases of overvoltage appearing on the communication lines. Typically these overvoltage protection devices incorporated the carbon block type which provided a parallel air gap so that if the gas tube should fail some type of back-up air gap would be provided until the gas tube could be replaced. However, the carbon block protector during normal operation on the communication line causes static to appear on the line and thus, later protection devices used thermally sensitive plastics which were assembled with spring pressure on them and thus when overheated would yield and short the terminal line to ground.
With the inherent desire to protect the communication equipment several different types of protectors have been used over the years, each including thermally active members which when overheated causes the line terminals to short to ground. Initially the thermally sensitive material was a low temperature melting solder pellet, which when melted because of extreme heat caused by an overvoltage, would permit the housing in some manner to short the line terminal to ground. Further improvements in the state of the art replaced the solder pellet used with the gas filled tube. Still further improvements of the protection devices, which proved to be more reliable utilized a back-up air gap together with the thermally sensitive material used for overheating protection in the assemblies.
However, all of these devices known in the prior art required that the technician in replacing any of the components after lightning strike or overvoltage condition to carefully replace the components as it was originally assembled so that the protection would be restored. This type of assembly work performed in the field proved to be a handicap and thus it was found more desirable to provide a device which is completely sealed and when it has provided its useful protection is just thrown away and replaced with a new unit. This, of course, became feasible only with the advent of inexpensive thermally sensitive plastics and a new type of construction which reduced the cost of the protection device.
Therefore, it is an object of the present invention to provide a miniature station protector module for communication systems which is completely sealed and may be disposed of once it has served its purpose for protecting the communication line.
It is another object of the present invention to provide a miniature station protector module which combines all of the features of the earlier type devices including fail-safe shorting, with a back-up air gap arrangement that is integral, axially aligned with the line terminals, highly stable and efficient, as well as, being inexpensive to manufacture.
It is still a further object of the present invention to provide a miniature station protector module which is capable of using a gas tube surge protector device as well as, solid state protector devices.
The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying drawing which forms a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the are to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims. Like reference characters have been utilized to designate like or corresponding components in the alternative embodiment of the invention in order for the reader to better understand the invention.